Synthesis, characterization and evaluation of copper nanoparticles as agrochemicals against Phytophthora spp.

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SCIENCE AND TECHNOLOGY DEVELOPMENT JOURNAL
NATURAL SCIENCES, VOL 2, ISSUE 6, 2018

Synthesis, characterization and evaluation of
copper nanoparticles as agrochemicals against
Phytophthora spp.
Hoang Minh Hao, Cao Van Du, Duong Thi Ngoc Dung, Cao Xuan Chuong,
Nguyen Thi Phuong Phong, Nguyen Huu Tri, Pham Thi Bich Van

1 INTRODUCTION
Abstract—By using water as a solvent, copper
nanoparticles (CuNPs) have been synthesized from
copper sulfate via chemical reduction method in the
presence of trisodium citrate dispersant and
polyvinylpyrrolidone (PVP) as capping agent. The
effects of the experimental parameters such as the
concentration of reducing agent (NaBH4), reaction
temperature, molar ratio of citrate/Cu2+ and weight
percentage ratios of Cu2+/PVP on the CuNP sizes
were studied. The size of CuNPs in a range of 31
nm was obtained at NaBH4 concentration of 0.2 M,
50oC, citrate/Cu2+ molar ratio of 1.0 and Cu2+/PVP
weight percentage of 5%. The colloidal CuNPs were
characterized by using UV–Visible spectroscopy,
transmission electron microscopy (TEM), and X-ray
diffraction (XRD) techniques. The colloidal solution
of CuNPs (3±1 nm) was investigated the potential
against Phytophthora spp. which cause economically
crop diseases. Under in vitro test conditions, the

inhibition of Phytophthora spp. mycelia growth at
three concentrations of CuNPs (10, 20, 30 ppm) after
48 hours are 90.18%, 91.87% and 100%,
respectively. These results provided a simple and
economical method to develop the CuNPs-basedfungicide.
Index
Terms—antifungal
activity,
citrate
dispersant, copper nanoparticles, Phytophthora spp.,
PVP

Received: 12-11-2017; Accepted: 22-01-2018; Published:
31-12-2018
Hoang Minh Hao1,*, Cao Van Du2, Duong Thi Ngoc Dung2,
Cao Xuan Chuong2, Nguyen Thi Phuong Phong3, Nguyen Huu
Tri4, Pham Thi Bich Van4 – 1Faculty of Chemical and Food
Technology, HCMC University of Technology and Education,
2
Faculty of Pharmacy, Lac Hong University; 3Faculty of
Chemistry, University of Science, VNUHCM; 4Faculty of
Science, Nong Lam University.
*Email:

I

n recent years, nanoparticles have been
extensively studied due to their unusual
chemical and physical properties [1, 2]. The
effective applications of the nanoparticles

generally depend on their size, shape and
protecting agents which could be controlled by the
preparation conditions [3]. A number of different
approaches to prepare metal nanoparticles such as
Cu, Ag, Pt, Au have been reported. Some of these
methods include photoreduction, chemical
reduction using reducing agents in association
with protecting agents [4-6].
Interestingly, the nanoparticles strongly
exhibited the antifungal and antimicrobial
activities [5, 6]. Among them, copper
nanoparticles (CuNPs) have much attention.
CuNPs showed a significant antifungal activity
against various plant pathogenic fungi such as
Phytophthora, Corticium salmonicolor [7].
Phytophthora is a genus of plant-damaging
Oomycete whose member species are capable of
causing enormous economic losses on crops. The
genus Phytophthora approximately includes one
hundred species [8]. Phytophthora spp. cause
diseases such as blight, stem rots, fruit rots.
Worldwide crop losses due to Phytophthora
diseases are estimated to be multibillion dollars
[9]. Synthetic chemicals are currently used for
inhibiting this fungal growth. However,
Phytophthora spp. are known to be able to
develop the resistance to chemicals rapidly [10].
Thus, the discovery of new alternatives with

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CHUYÊN SAN KHOA HỌC TỰ NHIÊN, TẬP 2, SỐ 6, 2018
lower risk of resistance plays a major role for
controlling the pathogens as Phytophthora spp.
As mentioned, CuNPs showed a significant
antifungal activity against Phytophthora. In
addition, the cost to produce CuNPs is much
cheaper than the others such as silver
nanoparticles (AgNPs) and gold nanoparticles
(AuNPs). However, the studies on antifungal
activity of CuNPs have not yet received much
attention in Vietnam. The low cost to prepare the
CuNPs is an advantage to use them in agriculture
as agrochemicals. In this study, CuNPs were
prepared in water by chemical reduction method
in the presence of the sodium citrate dispersant
and polyvinylpyrrolidone (PVP) as protecting
agents. The effects of the experimental parameters
such as the concentration of reducing agent
(NaBH4), reaction temperature, molar ratio of
citrate/Cu2+ and the weight percentage ratios of
Cu2+/PVP on the size of the CuNPs were
investigated.
UV–Visible
spectroscopy,
transmission electron microscopy (TEM) and Xray diffraction (XRD) techniques were used to
characterize CuNPs. The antifungal activity
against the growth of Phytophthora spp. mycelia
was estimated under in vitro conditions on Potato
Dextrose Agar (PDA) medium.

2 MATERIALS AND METHODS
Materials
Copper (II) sulfate (CuSO4, 99.0%),
polyvinylpyrrolidone (Mw 58,000 g/mol),
trisodium
citrate
dihydrate
(HOC(COONa)(CH2COONa)2.2H2O,
99.0%),
sodium borohydride (NaBH4, 98%) were
purchased from Acros Organics. All reagents
were used without further purification. Distilled
water was used as a solvent. Phytophthora spp.
were supplied by Laboratory Applications in
Microbiology, Institute of Tropical Biology,
Vietnam Academy of Science and Technology,
Linh Trung, Thu Duc, Ho Chi Minh City.
Synthesis of CuNPs
The mixture including PVP (0.2 g), CuSO4 and
HOC(COONa)(CH2COONa)2.2H2O
was

49

dissolved in 30 mL water. The mixture was heated
and stirred for 5 minutes. The Cu2+ ions in the
reaction mixture were then reduced to copper
metal by the introduction of NaBH4. As thermal
reduction proceeded, the blue solution turned to
red, indicating the formation of the CuNPs for 10

minutes.
Product characterization
UV–Vis absorption spectrum of the CuNPs
solution was measured by Jasco V670 (Jasco
Analytical Instrument). The colloidal CuNP
solutions were diluted in water with the same
concentrations prior to measuring UV-Vis spectra.
The UV-Vis spectra were scanned in a
wavelength range from 500 to 800 nm. TEM
images were measured by JEM-1400 version
(JEM-1400, JEOL). The samples for TEM
measurement were prepared by dropping CuNPs
solution onto a carbon-coated copper grid. The
histogram of the particle-size distribution and the
average diameter were obtained by measuring
particles. The XRD result was characterized using
D8 advanced Bragg X-ray (D8 Advance, Brucker)
with Cu Kα radiation. For sample handling, glass
slide was used as a substrate for measurement.
Leaned substrate was covered with the colloidal
CuNPs solution and dried in air.
Determination of the antifungal activity
The antifungal activity against Phytophthora
spp. was estimated by using the in vitro plate
dilution method. The colloidal CuNP solutions
with various concentrations (10, 20, 30 ppm) were
mixed with melting PDA medium to obtain a 15
mL total volume in Petri dishes. The control
dishes contained 50 ppm of PVP, or 50 ppm of
copper sulfate without colloidal CuNPs. The

fungus Phytophthora spp. strain was activated by
inoculation the mycelia on PDA dish at 37oC, 72
hours. Then, the activated fungus was split into
small pieces (5 mm x 5 mm). The treatments were
performed by putting the small piece of active
fungus in central of petri plates, wrapped with
parafilm and incubated at 37oC. The diameters of
the colony growth of the control and CuNP
samples were observed after 24 and 48 hours.
Each treatment for each concentration of CuNPs


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was replicated three times. The inhibition of the
growth of the mycelia was estimated by
measuring the colony diameter and calculated by
formula: growth inhibition (%) = (d1−d2/d1) ×
100, where d1 and d2 are colony diameters of the
control and CuNPs contained samples,
respectively
3 RESULTS AND DISCUSSION
Characterization of CuNPs
The formation of CuNPs is confirmed by the
powder X-ray diffraction (XRD). Figure 1
showing the peak positions with high crystallinity
at 43.2o, 50.4o, and 74.0o in XRD pattern are

consistent with metallic copper. These peaks
correspond to the typical face-centered cubic of
copper with miller indices at (111), (200), and
(220) which are in good agreement with the
literature values [5, 11-14]. This result also
indicated that copper oxides (Cu2O and CuO)
were not formed in the synthetic process.
Furthermore, the color of solution had changed
from blue to reddish. This observation revealed
that the efficiency of reduction of copper salt
(Cu2+, blue) into copper metal (Cu0, reddish) was
significant.

Fig 1. X-Ray diffractogram of CuNPs

Effect of reducing agent concentration on the
size of copper nanoparticles: Sodium borohydride
(NaBH4) was used as a reducing agent to prepare
CuNPs. Reaction temperature (50oC), and the
amount of PVP (0.2 g) were kept constant. The
amounts of copper salt and trisodium citrate were
used to ensure that the weight percentage ratio of
Cu2+/PVP and the molar ratio of citrate/Cu2+ were

always 3% and 0.5, respectively. The reaction
time was 15 minutes. The reducing agent of
NaBH4 allows a variation of concentration within
a range of 0.1 – 0.5 M. Figure 2 illustrated the
UV-Vis spectra of colloidal CuNP solutions with
various concentrations of NaBH4. The results

showed that the surface plasmon resomance of
CuNPs shifted to shorter wavelengths with
increasing the NaBH4 concentration (from 583 nm
at 0.1 M to 570 nm at 0.2 M). However, the
maximum absorption peaks shifted to longer
wavelengths (574, 576 and 582 nm) at higher
concentrations (0.3, 0.4 and 0.5 M) of reducing
agent.

Fig. 2. UV-Vis spectra of colloidal CuNP solutions at various
concentrations of NaBH4

This observation could be attributed to an
increase the CuNP sizes at higher concentrations
(> 0.2 M) [5, 6, 18]. The CuNPs were generated
in soltution through two stages. The copper nuclei
is firstly generated and then was the growth of
CuNPs [18]. It is thus important to control the
preparation process that copper nuclei must
generate faster and grow up slower. With
increasing the concentration of NaBH4, the
reaction conversion rate of copper sulfate
increased, the amount of copper nuclei rose, and
small particle size powders were obtained.
However, an excess number of copper nuclei
would be generated when the reducing agent
concentration was high. This resulted in an
agglomeration of nuclei and a growth of the
particle size. Thus, the optimal concentration of
NaBH4 was 0.2 M.

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Effect of reaction temperature on the size of
copper nanoparticles
Concentration of NaBH4 (0.2 M), the weight
percentage ratios of Cu2+/PVP (3%) and the molar
ratio of citrate/Cu2+ (0.5) were fixed in the
experiments. The reaction temperature was varied
in a range from 40 to 80oC. The UV-Vis spectra
of colloidal CuNP solutions were given in Figure 3.
The positions of maximum peaks had a decrease
in wavelength with increasing the reaction
temperature from 40 to 60oC (586 nm at 40oC,
575 nm at 50oC and 570 nm at 60oC). However,
an increase in temperature from 60 to 80 oC, the
opposite shifts was obtained (575 nm at 70 oC and
580 nm at 80oC). The results could be attributed
to the change of CuNP sizes with varying the
temperature. The CuNP size decreased when the
temperature grew up to a certain range. The
nucleation rate was greater than the growth rate
when the temperature increased within a range
from 40 to 60oC. At higher temperatures (> 60oC),
the viscosity of the solution decreased and the
growth rate enhanced due to CuNP collisions. As
a result, the size of CuNPs increased with the
increasing the reaction temperature [6, 18, 19]. At
lower temperatures, the formation of CuNPs was

not favorable. Therefore, the optimal reaction
temperature was selected at 50oC.

51

reducing agent (NaBH4) was 0.2 M, and the
amount of PVP was 0.2 g while the molar ratio of
citrate/Cu2+ varied in a range from 0.0 to 2.0.
Figure 4 depicted UV–Vis absorption spectra of
colloidal CuNP solutions in a range of molar ratio
of citrate/Cu2+ from 0.0 to 2.0. In the presence of
citrate dispersant, the maximum peaks of CuNPs
shifted to shorter wavelength with increasing
molar ratio of citrate/Cu2+. This observation could
result from a change in nanoparticle size.
However, absorbed wavelengths ( 567 nm) were
insignificantly different when using molar ratios
ranging from 1.0 to 2.0.
Effect of the weight percentage ratio of copper
salt to PVP on the size of copper nanoparticles
During the synthetic process, the reaction
temperature (50oC) and the reducing agent
concentration (0.2 M), and the amount of PVP
(0.2 g) were kept constant. The weight percentage
ratios of Cu2+ to PVP were varied in a range from
1 to 13%. The amount (mole) of citrate was also
varied according to the variation of the copper salt
amount in solutions so that the molar ratio of
citrate/Cu2+ (1.0) was always constant. The UVVis spectra of the CuNP solutions were given in
Figure 5. The results showed that the absorbance

at maximum peaks increased with increasing the
weight percentage ratio of Cu2+ to PVP from 1 to
11%. The position of the maximum peaks in a
region of 567–570 nm. When the Cu2+/PVP ratio
reached 13%, the peak shifted to longer
wavelength (573 nm). This result showed that the
size of CuNPs increased at the Cu2+/PVP ratio of
13%.

Fig. 3. UV-Vis spectra of colloidal CuNP solutions at different
temperatures

Effect of citrate/copper salt ratio on the size of
copper nanoparticles
In order to investigate the effect of citrate/Cu2+
ratios on the size of CuNPs, the reaction mixture
was conducted at 50 oC, the concentration of

Fig. 4. UV-Vis spectra of the colloidal CuNP solutions with
different molar ratios of citrate/copper salt.


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TEM images of samples

Fig. 5. UV–Vis spectra of colloidal CuNP solutions with
various weight percentage ratios of Cu2+ to PVP.

The TEM images of CuNPs shown in Figure 6
confirmed the correlation between the citrate
concentration and the size of the produced
CuNPs. The changes of size caused the UV-Vis
spectra to shift to shorter wavelengths as mention
above. In the absence of citrate, average diameter
of CuNPs was in a range of 207 nm, whereas its
diameter appeared in a range of 31 nm at molar
ratio of citrate/Cu2+ of 1.0. Thus, this ratio of
citrate to copper salt was optimized at 1.0 to
prepare CuNPs for biological tests. Moreover,
these results confirmed that CuNPs with smaller
sizes absorb at shorter wavelengths in UV–Vis
spectra.

Fig. 6. TEM images of CuNPs prepared in the absence (a) and the presence (b) of citrate dispersant. The molar ratio of
citrate/Cu2+ is 1.0

Fig. 7. TEM images of CuNPs prepared in various ratios of Cu 2+/PVP: (a) 5%, (b) 9% and (c) 11%


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Figure 7 showed the TEM images and size
distribution of the copper nanoparticles which
were synthesized with different of ratio of
Cu2+/PVP. At ratio of Cu2+/PVP=5% (Fig. 7a), the
copper nanoparticles were synthesized mainly in
spherical, uniform distribution with the size 3 ± 1

nm. When the ratio of Cu2+/ PVP increased to 9 %
and 11% (Fig. 7b, 7c), the copper nanoparticles
were prepared in an approximate spherical shape,
higher concentration and cluster formation
because of high concentration of nanoparticles
formed. However, due to the synergistic of PVP
and citrate, the nanoparticles were prepared with
small size, the size in range of 4±1 nm and 3±1
nm, respectively.
Synergistic effect of citrate dispersant and
PVP capping agent: Polyvinylpyrrolidone (PVP)
has been extensively used as a capping polymer to
protect colloidal solution containing metallic
nanoparticles [5, 6]. However, the bulky polymer
is ineffective to coat all surfaces of the metallic
nanoparticles. These results in an outgrowth in
size of particles were due to their collision. To
prevent this disadvantage, a molecular protecting
agent like trisodium citrate could be used. A
certain amount of trisodium citrate molecules is
adsorbed on the surface of metallic nanoparticles.
As a consequence, the aggregation of
nanoparticles due to their collision was
significantly reduced. Furthermore, it has been
hard to prepare these small and uniform-sized
metallic nanoparticles in the sole presence of
capping polymers or citrate dispersant [6]. The
synergistic effect of citrate dispersant and capping
polymer has been expected to control size growth
of CuNPs as demonstrated in Figure 8. Citrate and

PVP work as size controller and polymeric
capping agents, because they hinder the nuclei
from aggregation through negative charge and
polar groups, which strongly absorb the CuNPs on
the surface via electrostatic interactions
coordination bonds [15, 16].

53

Fig. 8. A demonstration of the synergistic effect of citrate
dispersant and PVP capping polymer on controlling size
growth of CuNPs. Left figure depicts the formation of
complexes of copper ions and citrate or PVP. The synergistic
effect of citrate and PVP is given in the right figure.

Stability of colloidal CuNP solutions: The
colloidal CuNP solutions were synthesized by
using optimized conditions described above.
Figure 9 showed that the positions of peaks at
maximum absorption wavelengths (569 nm) were
not changed after 1 and 3 months of storage. This
observation confirmed that the CuNPs were stable
during storage time, i.e., the size of CuNPs was
not changed. However, the maximum peaks
shifted to 579 nm after 5 and 6 months. This result
revealed that the size of CuNPs increased with
increasing the storage time. Furthermore, there
was no peak of Cu2O at 450 nm, i.e., the CuNPs
were not oxidized during the storage period.

Fig. 9. UV-Vis spectra of the colloidal CuNP solutions at
different storage times


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CuNPs inhibit Phytopthora spp. in vitro
Basing on optimized experiments above, the
CuNPs having an average diameter in range of
31 nm were prepared. The potential of the
colloidal
CuNP
solutions
at
various
concentrations (10, 20, 30 ppm) were estimated
against Phytophthora spp. Figure 10 showed the
antifungal ability against Phytophthora spp. After
48 hours of the incubation, the highest antifungal
activity was observed at the CuNP concentration
of 30 ppm (100%). At lower concentrations of 10
ppm and 20 ppm, CuNPs were less effective with
90.18% and 91.87% of fungal growth inhibition,
respectively.

Fig. 10. The fungal growth inhibition of CuNPs at various
concentrations against Phytophthora spp. after 48 hours of

incubation. CuNPs were not added to control

Nanoparticles can be currently used as
alternatives to chemical pesticides. Most of CuNP
studies have focused on antibacterial activities
and to a lesser extent on antifungal activities.
Under in vivo condition, the chromosomal DNA
degradation in E. coli started within 30 minutes of
treatment with CuNPs, and more degradation
occurred with the increasing of the nanoparticle
exposure time. The mechanism of antibacterial
activity of CuNPs in E. coli cells has been
proposed. The copper ions (Cu2+) attributed to be
the main effector for DNA degradation, the
nascent ions were generated from the oxidation of
metallic CuNPs when they were in the vicinity of
agents, namely cells, biomolecules or medium

components [17]. To the best of our knowledge no
study has been reported to explore the mechanism
of the growth inhibition of CuNPs on
Phytophthora spp.
4 CONCLUSION
CuNPs were prepared via chemical reduction
method under the presence and the absence of
citrate dispersant and PVP capping polymer. The
purity and stability of the CuNPs were revealed
by
X-ray
diffraction

(XRD),
UV–Vis
spectroscopy and TEM techniques. The effects of
the concentration of reducing agent, the reaction
temperature and the ratios of copper salt to
protecting agents on the CuNP sizes were
investigated. In order to obtain a small size
distribution (31 nm), the experimental conditions
were optimized. The optimal concentration of
NaBH4, and reaction temperature were 0.2 M and
50oC, respectively. The ratios of Cu2+ to citrate
(citrate/Cu2+-molar ratio) and PVP (Cu2+/PVPweight percentage) were 1.0 and 5%, respectively.
In solution, citrate and PVP played as size
controller and capping agents, they impeded the
aggregation of CuNPs by forming coordination
bonds via negative charge and polar groups. The
CuNPs having the size of 31 nm were estimated
the inhibition of the fungal growth and exhibited a
high potency of the antifungal against
Phytophthora spp. under in vitro treatments. The
result showed a complete inhibition of the
Phytophthora spp. mycelia growth at 30 ppm.
This result demonstrated that CuNPs not only
were used as alternatives to chemical pesticides
against Phytophthora spp. without any
phytotoxicity but also can be applied as a novel
antifungal agent in agriculture to control the plant
pathogenic fungi.
Acknowledgment: The authors are thankful
to Lac Hong University and Ho Chi Minh City

University of Technology and Education for
support.
Laboratory
Applications
in
Microbiology, Institute of Tropical Biology,
Vietnam Academy of Science and Technology,
Linh Trung, Thu Duc, Ho Chi Minh City is
gratefully acknowledged.


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Tổng hợp, xác định cấu trúc hóa học và
khảo sát hoạt tính kháng nấm
Phytophthora spp. của hạt đồng nano
Hoàng Minh Hảo1,*, Cao Văn Dư2, Dương Thị Ngọc Dung2, Cao Xuân Chương2,
NguyễnThị Phương Phong3, Nguyễn Hữu Trí4, Phạm Thị Bích Vân4
Khoa Công nghệ Hóa học và Thực phẩm, Trường Đại học Sư phạm Kỹ thuật TP. HCM,
Khoa Dược, Trường Đại học Lạc Hồng, 3Khoa Hóa học, Trường Đại học Khoa học Tự nhiên, ĐHQG-HCM,
4
Khoa Khoa học, Trường Đại học Nông Lâm
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*Tác giả liên hệ:
Ngày nhận bản thảo: 12-11-2017; Ngày chấp nhận đăng: 22-01-2018; Ngày đăng: 31-12-2018
Tóm tắt—Các hạt đồng nano (CuNPs) đã được
tổng hợp trong dung môi nước bằng phương pháp
khử hóa học trong sự hiện diện của các tác chất
phân tán trisodium citrate và chất bảo vệ
polyvinylpyrrolidone (PVP). Ảnh hưởng của nồng
độ chất khử (NaBH4), nhiệt độ phản ứng, tỷ lệ mol
citrate/Cu2+ và tỷ lệ khối lượng Cu2+/PVP lên kích
thước các hạt đồng nano đã được khảo sát. Kích
thước 31 nm của các hạt đồng nano đạt được tại
nồng độ chất khử là 0,2 M, nhiệt độ phản ứng là
50oC, tỷ lệ mol citrate/Cu2+ là 1,0 và tỷ lệ khối
lượng Cu2+/PVP là 5%. Đặc điểm hạt đồng nano

được xác định bằng phổ tử ngoại-khả kiến (UV–
Vis), chụp ảnh dưới kính hiển vi điện tử truyền
qua (TEM) và nhiễu xạ tia X (XRD). Hoạt tính
kháng nấm của các hạt đồng nano (kích thước
31 nm) được thử nghiệm đối với nấm
Phytophthora spp. Thử nghiệm in vitro cho thấy,
chế phẩm đồng nano tại các nồng độ 10, 20 và 30
ppm đã ức chế 90,18%, 91,87% và 100% sự phát
triển của tơ nấm Phytophthora spp. sau 48 giờ.
Kết quả này là cơ sở để phát triển chế phẩm diệt
nấm đơn giản, kinh tế dựa trên các hạt đồng
nano.

Từ khóa—hoạt tính kháng nấm, chất phân tán citrate, hạt đồng nano, Phytophthora spp., PVP